1. Field of the Invention
The present invention relates to a photosensitive member serving as a latent image forming device, and more particularly, to an electrophotographic photosensitive drum serving as a photosensitive device integrated with an exposure source. Further, the present invention relates to an electrophotographic image forming apparatus using the electrophotographic photosensitive drum. Still further, the present invention relates to a method of manufacturing the electrophotographic photosensitive drum.
2. Description of the Related Art
In an electrophotographic process, a photosensitive member is uniformly charged and then exposed to light with a desired pattern based on image information so as to form a charge density distribution (latent image) on a surface of the photosensitive member. After that, the charge density distribution thus formed is developed with toner, to thereby obtain a visible image.
As a product to which the electrophotographic process is applied, a laser printer and an LED printer are widely used.
In the laser printer, a semiconductor laser is used as an exposure source, and a laser beam of the semiconductor laser is reflected by a rotating polygon mirror to thereby perform scanning on the photosensitive member.
In this case, in the following description, a main scanning direction of the rotary drum-shaped photosensitive member indicates a longitudinal direction of the drum (drum generatrix direction). Further, a sub-scanning direction of the rotary drum-shaped photosensitive member indicates a circumferential direction of the drum.
In the LED printer, there is employed a method in which the required number of light emitting diode (LED) pixels are arranged in a laser scanning direction (main scanning direction) of the laser printer, thereby forming an image on the surface of the photosensitive member by use of an imaging device.
The LED printer is characterized in that image positioning accuracy is enhanced because main scanning involved in the laser printer is not performed in the LED printer.
However, in both the laser printer and the LED printer, accuracy of sub-scanning is determined depending on a relative position and a relative speed between the photosensitive drum and the exposure source. Accordingly, unevenness in pitch is generated in a sub-scanning direction due to, for example, vibration of the exposure source, decentering of the photosensitive drum, and fluctuation in rotational speed.
In order to enhance the accuracy of the sub-scanning, it is possible to reduce a relative speed between the exposure source and the photosensitive member to zero. Specifically, it is possible that the exposure source and the photosensitive member are to be integrated with each other. As examples of the method of obtaining the integrated structure, the following methods have been employed.
(1) An example of a flat-plate photosensitive device is one in which a photoconductive layer is stacked on a light emitting device through an intermediate buffer layer.
Japanese Patent Application Laid-Open No. H05-221018 discloses introduction of the intermediate buffer layer, as a method of stacking an a-Si photoconductive layer (amorphous silicon photoconductive layer) with high hardness on a thin-film electroluminescence (EL) layer.
(2) An example of a flat-plate photosensitive device is one in which an a-Si photoconductive layer is stacked on a light emitting array layer through an insulating layer.
Japanese Patent Application Laid-Open No. H06-095456 discloses a top emission structure of an inorganic LED in which a pixel thin-film-transistor (TFT) matrix is formed on a glass substrate.
(3) An example of a photosensitive drum in which a photoconductive layer is stacked on an electroluminescence (EL) device including a pixel TFT.
Japanese Patent Application Laid-Open No. 2001-018441 discloses a device transfer process as a method of forming the EL device including a TFT layer on a cylindrical substrate.
In this case, the rotary drum-shaped photosensitive member, in which the exposure source and the photosensitive member are integrated with each other, that is, the drum integrated with the exposure source, in which pixels are formed on the photosensitive member so as to eliminate the factor of deviation in positional accuracy of an image not only in the main scanning direction but also in the sub-scanning direction, is hereinafter referred to as a digital photosensitive drum.
It is appropriate for a direction of technical development to employ the method of using the digital photosensitive drum in view of the technical transition from point scanning with a laser beam to an LED array in which the main scanning direction is fixed, and further, from the LED array to a pixel matrix system in which the sub-scanning direction is also fixed.
However, in view of a use mode as a printer, the conventional digital photosensitive drum system is inconvenient in terms of continuous printing. Note that the continuous printing of this case relates to a small-diameter drum (drum perimeter<print length area) or the like used in a case of continuous printing on a consecutive sheet (for example, roll paper) and printing on a cut sheet.
This is because, in the structures disclosed in Japanese Patent Application Laid-Open Nos. H05-221018 and H06-095456, a device having the flat-plate exposure source and the photosensitive member which are integrated with each other is used, thereby making it difficult to deal with the continuous printing.
Further, in the structure of the digital photosensitive drum disclosed in Japanese Patent Application Laid-Open No. 2001-018441, a self-luminous device is wound around the drum substrate, so a seam is formed in the circumferential direction of the drum. Specifically, as illustrated in FIG. 3 of Japanese Patent Application Laid-Open No. 2001-018441, when a planar pixel array is formed and then the pixel array is bonded on a cylindrical substrate, a seam is inevitably formed. For this reason, in the seam portion, the pixel array is formed in a discontinuous manner, which causes an image defect. As a result, printing cannot be performed on a continuous area larger than the drum perimeter.